In recent years, composite resins have been developed for the treatment of carious teeth, as a replacement for dental cements such as zinc phosphate cement, silic acid cement and the like, and there have recently been produced composite resins showing stable water absorbability and low disintegratability over a long period and having substantially the same color tone as natural teeth. Composite resins, however, do not essentially adhere to the enamel and dentin of the teeth; therefore, during the long use of the composite resin, a gap is formed between the tooth and the composite resin used as a filler, secondary caries tend to arise, and in some cases the composite resin was detached. There have heretofore been developed various adhesion improvers such as adhesive liner and the like, for improvement of the adhesion between the composite resin and the cavity wall, and further there have been proposed dental adhesive compositions having adhesivity to the tooth, such as adhesive filler for prevention of caries, orthodontic adhesive and the like.
However, only part of these conventional products maintains strong adhesion to the teeth over a long period in a circumstance (e.g. inside the mouth) which is wet and shows severe temperature change. For example, there was developed an adhesive composed mainly of an .alpha.-cyanoacrylate, to use as a filler for prevention of caries and an orthodontic adhesive both having adhesivity to the teeth. However, the adhesive is said to have problems in durability inside the mouth as well as in handleability during use.
Meanwhile, in recent years there has been widely used a filler which uses a resin composed mainly of bisphenol A diglycidyl methacrylate and wherein the resin is to be cured with a benzoyl peroxide-amine type catalyst. This filler, however, has no adhesion to the dentin and the enamel, therefore, when filled in dental cavities, is detached after a little while and induces the formation of secondary caries.
Also, an adhesive comprising 2-methacryloyloxyethyltrimellitic acid anhydride has been proposed as an adhesive having excellent water resistance and durability and well withstanding the inside-the-mouth use. However, the catalyst for normal temperature polymerization, used in the adhesive is ordinarily restricted virtually to tri-n-butylborane oxide; therefore, the adhesive, although having strong adhesion to the dentin of the teeth, is slow in polymerization reaction rate, requires ten and odd minutes up to the completion of curing, is very unstable in the air making its handling difficult; thus, the adhesive has many problems from the standpoint of clinical dentistry.
As described above, there has been found yet no dental material having adhesion to both the dentin and the enamel and maintaining strong adhesion over a long period even in an inside-the-mouth circumstance which is wet and shows severe temperature change.
In view of the above prior art, the present invention is intended to provide a dental adhesive which has physical and engineering properties required for dental adhesives, for example, hardness, compression strength, water resistance, etc. and which further has excellent adhesion to the dentin and the enamel.